This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
Amine-boranes have gained considerable importance as potential candidates for hydrogen storage. Moreover, they have been evaluated as reagents in organic chemistry and materials chemistry. (Carboni and Monnier, Tetrahedron, 1999, 55, 1197; Staubitz, et al., Chem. Rev. 2010, 110, 4023) Amine-boranes have also shown promise as safe energetic materials. (Ramachandran et al., Chem. Eur. J. 2014, 20, 16869)
Current approaches to amine-boranes from amines include exchange with borane-Lewis base complexes or metathesis of alkylammonium salts with metal borohydrides. The former necessitates the use of moisture-sensitive and pyrophoric borane-tetrahydrofuran (BTHF) or borane-dimethyl sulfide (BMS), or harsh reaction conditions with the stable borane-ammonia complex (AB). The poor solubility of sodium borohydride and alkylammonium salts in common organic solvents severely restricts the generality of the metathesis protocol. To circumvent these, we recently discovered and disclosed a scalable protocol to access amine-boranes via an in situ generation of carbonic acid from sodium bicarbonate and water (Ramachandran et al., U.S. Patent application 2016/0101984, dated Apr. 14, 2016).
Despite these advances in their synthesis and application, borane complexes of amines bearing functional groups are rare. This also restricts the use of borane as an amine-protecting group for organic chemistry applications. Thus, a convenient approach to functionalized amine-boranes would be highly appreciated by the scientific community.